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Pb de communication between trans and rcvr

ello there,

Now that I ve gathered all the parts, I've tried to connect everything together but it doesn't work!!!   ;(

I've got;

Transmitter : old futaba  fp t7fg/k (found in a boot fair but working, apparently.. got battery signal)

Receiver : PCM 1024 FP-R1299DP

Both with a crystal t27 35.060 Mhz

One servo Futaba JR UK 3001

One battery 6V  4.5Ah


The thing is I have no idea if I have to set up my transmitter in order for it, to send the signal to the receiver, then to the servo.

I 've attached a picture of my installation that we can see where I am mistaken, hopefully.

Thanks for your help guys as it's my first step in electronic.

All the best!




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According to the TX manual page 5/19, ur TX sld be AM.


Did some search on PCM:

"PCM (pulse code modulation) essentially sends strings of numbers, representing the position of the sticks and knobs on a transmitter, to the FM transmitter module, the thing that plugs into the back of the transmitter. These numbers are decoded in the receiver to move the servos if the numbers are checked to be valid. The decoded information that goes to each servo is in the form of a pulse that uses 1.5 miliseconds equal to neutral.

PPM (pulse position modulation) serves the same purpose as PCM, however, it differs in that it does not use a string of numbers but produces a sync pause in each frame before the information for each channel is sent via the FM transmitter module. A frame contains the sequential information for each channel. The frame is repeated over and over. Each channel is pulse width modulated with 1.5 miliseconds being equal to neutral.

Manufacturers commonly refer to PCM and FM, instead of PCM and PPM, which is a bit eroneous but that's the way most people understand it. In a similar way, doctors refer to anti-coagulants as blood thinners. These medications don't change the viscosity of the blood, they just help in preventing the blood from clotting. But, that's the way the public understands it."


n for dual conversion xtals:

"In a dual conversion receiver there are two crystals, the one we change to change channels and a fixed crystal. The idea is that by reducing the frequency of the incoming signal down to the IF frequency in two stages we can increase receiver selectivity and overcome the theoretical problem associated with single conversion Rxs mentioned above. The first crystal (the one we plug in) produces a signal between 24 and 25Mhz whilst second produces a 10.7Mhz signal to be mixed with the difference of the incoming signal and the first oscillator signal i.e. 35Mhz - (24-35Mhz). The difference in these two signals (455 or 470Khz) is then fed to the IF strip as before. Because Dual Conversion receivers are more complicated than single conversion receiver they are more expensive. Also as a rule Dual Conversion Rxs need to be fitted with cyrstals of the same make as the Rx which is not always the case with single conversion Rxs."


I'm new to RC myself, only get to use them for my sch projects. you might have wanna post on rc forums and the above forum, before looking for the xtals. There are ppl collecting these TX & RX. I've read some good reviews about the RX though.


Btw, ur system (7ch TX + 9ch RX )is kinda overkill if you want to control 1 servo.

I appreciate the manuals as well! :)
I bought those crystal (35mhz) because one of them was already in the transmitter itself, moreover, my transmitter seems to be FM and not AM, there is a label on the front of it that you can see on the pic.
Do you still I should change receiver??? or just the crystals? In fact I'd rather keep the Tx.
Kind regards

Here's 2 manuals for ur transmitter (Pg 5) and receiver (Pg 5).


I was wrong with the Tx Freq, it sld be 27, 72 to 76 MHz

There's also a difference in modulation: TX is AM, RX is PCM (not sure wat tat means).

I guess u can try it with a pair of 72 MHz crystals for dual conversion?


Lastly, here's wat i found on another forum:

"The original R129DP receivers have difficulty talking to some 9-channel transmitters. They would not respond at all to certain types of transmitters used. This was corrected around 1999. If you are unsure if your receiver is updated, you can simply send it to us and we will check it. If you are comfortable doing so, you can take the receiver out of the case and check the letters on the large decoder I.C. On the updated receivers the I.C. letters will read FP6302B. On receivers that are not updated the letters are FP6302 no B designation. (Note that we cannot be responsible for the workmanship of the user. If you are unsure how to open your case and check, please send the receiver for service.)"

All right guys, thank you for your suggestions!

I thought so it was a plug and play..but yes, if there is a pb of frequency, ..Obviously!

The thing is, when I bought the receiver, nothing was specified, no instructions either..

Hold on, sorry, check out the description of the ad on ebay :

''Futaba PCM 1024 FP-R129DP 9 channel 35 Mhz Receiver



So, doesn't it mean that the receiver is working on 35 Mhz???

Both of my crystal are in 35Mhz, so what the !!...... problem!

Thanks again guys for your time!


Ps; On the final result, I want to operate my servo via my transmitter.

the RC transmitter is a plug-n-play device.

1) Extend antenna

2) Check trimming knobs, if any

3) Check crystal

4) On power and check battery status

5) Play =D


tatz how my 2-ch Futaba system works. so if it still fails, time to look at other aspects, i.e. receivers, etc.

If ur receiver is FR-R129DP, then u're using the wrong crystals. Ur're receivers can only operate with 50 & 72 MHz crystals.


As for the transmitter, i think it's working on 35 MHz based on this site. So either one have to go.


Here's a good site to get cheap radio systems.

Hi again guys,

I still don't have any answer after few day and so, stucked with my project..

Am I not clear enough with my description?

Please , be kind enough to help me solving this pb



Your post is assuming we understand exctly what it is you want to achieve. And how the wires are connected. You fail to describe what you tried yourself to solve the problem. And your photo should be embedded, not attached. We hate clicking. That's how lazy we (internets peoples) are ;-)

Also, we need you te have patience. We are all hobbyists with burning questions. Sometimes we have time to spare on solving yours.

Here is some tips to get you started. Report the results back to us, even if it solves your problem.

- make sure your batteries are all charged to te right voltage. Use a multimeter.
- google your hardware, all of it. find manuals and datasheets.